The invention relates to a filling level sensor for a liquid container, in particular a fuel container for a motor vehicle, having a lever arm supporting a float, having a support, provided for fastening in the liquid container, for bearing the lever arm, and having a detecting device for detecting the position of the float.
Such level sensors are used in fuel containers of present day motor vehicles and are known from practice. In order to compensate raising and lowering of the bottom of the fuel container, the support of the known liquid level sensor is fastened on a component, such as a splash part, for example, prestressed against the bottom of the fuel container. The aim of this to ensure that the position of the float corresponds to the filling level in the liquid container.
It is disadvantageous in the known filling level sensor that because of the large spacing between the region prestressed against the bottom and the swiveling region of the float, it is impossible to determine the zero position of the lever arm reliably. In addition, the detection of the zero position of the float is rendered difficult by the fact that the component on which the support is fastened can tilt, or that the angle of inclination of the component holding the support changes upon warping of the bottom. Consequently, the filling level in the liquid container cannot be determined reliably with the aid of known filling level sensor. In particular, present day fuel containers made from plastic can be deformed strongly on thermal expansions and as a function of the filling level.
The invention is based on the problem of configuring a filling level sensor of the type mentioned at the beginning such that it can determine with particular accuracy the filling level in a fuel container, in particular.
According to the invention, this problem is solved by means of a second lever arm, provided for the purpose of prestressing against a bottom of the liquid container in the region of the float, and by a detecting device for determining the position of the second lever arm.
Owing to this configuration, the filling level in the liquid container can be determined with particularly high accuracy by determining the difference between the positions of the lever arms. Since the second lever arm determines the position of the bottom in the region of the float, a slightly tilted arrangement of the support leads only to unimportant falsifications of the filling level determined. The filling level in the fuel container can thereby be detected with particular accuracy. A further advantage of this configuration consists in that the support need no longer be fastened on a component prestressed against the bottom, as in the case of the known liquid level sensor. The support can thereby be fastened directly on the wall of the liquid container. Particularly in the case of fuel containers constructed as a multichamber tank, this leads to a substantial simplification in assembly, since in this case each of the chambers requires a filling level sensor.
The detecting device for the second lever arm could have a potentiometer, for example. Such potentiometers are, however, difficult to protect against the chemical influences of the liquid, and are therefore very vulnerable. However, in accordance with an advantageous development of the invention, electric contacts of the detecting device can simply be encapsulated against the liquid in the liquid container, when the second lever arm is shaped for adjusting at least one magnet and when the detecting device has a magnetic sensor. Passive magnetic position sensors such as are disclosed in DE 196 48 539 A1 could be used, for example, as magnetic sensor. Moreover, however, Hall elements, reed contacts or similar sensors are also conceivable. The sensors have the advantage that they are capable of diagnosis. In addition, for example, reference points can be interrogated or calibrated by an appropriate configuration of an electronic system of the detecting device.
The filling level sensor according to the invention could, for example, have a second detecting device for detecting the deflection of the second lever arm. However, the filling level sensor according to the invention requires only a single detecting device when the detecting device is shaped for determining the difference in the deflections of the lever arms.
In accordance with another advantageous development of the invention, the detecting device for determining the difference between the deflections of the lever arms is of a particularly simple structural configuration when magnets which can be adjusted by the two lever arms are respectively situated opposite one another with opposite polarization, and when the magnetic sensor is arranged between the range of movement of the magnets.
The filling level sensor according to the invention requires particularly few components to be mounted when the second lever arm has a lever wire which is angled off to form a bearing axis of the bearing in the support.
Damage to the bottom of the liquid container by the second lever arm can be avoided in a simple way in accordance with another advantageous development of the invention when the lever wire has a bend in its region provided for bearing against the bottom. The bottom of the liquid container can additionally have a slideway.
Since the liquid container, in particular the fuel container, is frequently a container of complicated shape, the relationship between filling level and filled amount in the container is not linear. The determination of the filled amount with the aid of the filling level sensor according to the invention requires a particularly low outlay when the second lever arm has a cam disk for adjusting the magnet.
In accordance with another advantageous development of the invention, it is easy to ensure that the second lever arm bears reliably against the bottom, and that the magnet bears reliably against the cam disk when the magnet of the second lever arm is prestressed indirectly or directly against the cam disk.
The number of the components of the filling level sensor according to the invention which are to be mounted can be kept particularly low when the magnet of the second lever arm is instructed as a cam disk.
A contribution to further simplifying the design of the filling level sensor according to the invention is made when the support has a flange, which can be inserted in an opening in the fuel container, and in each case guides for the magnets of the lever arms, and a cutout, which is sealed off from the fuel container and serves to hold the magnetic sensor. Furthermore, this contributes to simplifying the mounting of the filling level sensor according to the invention in the liquid container.
The mounting of the filling level sensor according to the invention is particularly simple when the lever wire has a bend in the region of the cam disk, and when the cam disk is clipped to the lever wire.